1. Field of the Invention
The present invention relates to novel propoxylate-containing fuel compositions and novel additive concentrates.
2. Description of the Background
Carburetors and intake systems of gasoline engines as well as injection systems for fuel metering in gasoline and diesel engines are increasingly being contaminated by impurities. The impurities arise from dust particles from the air taken in by the engine, unburnt hydrocarbon residues from the combustion chamber and the vent gases from the crank case which are passed into the carburetor.
These residues shift the air/fuel ratio during idling and in the lower part-load range so that the mixture becomes richer and combustion less complete. As a result of this, the proportion of uncombusted or partially combusted hydrocarbons in the exhaust gas increases and the gasoline consumption rises.
It is known that these disadvantages are avoided by using fuel additives for keeping valves and carburetor or injection systems clean (cf. for example: M. Rossenbeck in Katalysatoren, Tenside, Mineralöladditive, editors J. Falbe, U. Hasserodt, page 223, G. Thieme Verlag, Stuttgart 1978). A distinction is now made between two generations, depending on the mode of action and preferred place of action of such detergent additives. The first generation of additives could only prevent the formation of deposits in the intake system but could not remove existing deposits. On the other hand, the additives of the second generation can prevent and eliminate deposits (keep-clean and clean-up effect). This is permitted in particular by their excellent heat stability in zones of high temperature, in particular at the intake valves.
The molecular structural principle of these additives of the second generation which act as detergents is based on the linking of polar structures with generally higher molecular weight nonpolar or oleophilic radicals.
Typical members of the second generation of additives are products based on polyisobutene in the nonpolar molecular moiety, in particular additives of the polyisobutylamine type. Such detergents can be prepared by two different multistage synthesis processes, starting from polyisobutenes: the first process takes place via chlorination of the polymeric parent structure, followed by nucleophilic substitution of the polymeric parent structure by amines or preferably ammonia. The disadvantage of this process is the use of chlorine, which results in the occurrence of chlorine- or chloride-containing products, which is now by no means desirable. In the second process, the polyisobutylamines are prepared starting from polyisobutene, by hydroformylation and subsequent reductive amination according to EP-A-0 244 616.
Detergent additives, which may originate from a large number of chemical classes of substances, are used in general in combination with a carrier oil. The carrier oils have an additional “washing function”, often support and promote the detergents in their action and can help to reduce the required amount of detergent. Specific detergents do not display their action at all until they are combined with a carrier liquid. Usually, viscous, high-boiling and in particular heat-stable liquids are used as carrier oils. They coat the hot metal surface (for example the intake valve) with a thin liquid film and thus prevent or delay to a certain degree the formation or deposition of decomposition products on the metal surfaces, but without being able to replace the detergent additive components.
Suitable carrier oils for the fuels for internal combustion engines are, for example, high-boiling refined mineral oil fractions, as well as synthetic liquids. Suitable mineral carrier oils are, for example, fractions obtained in mineral oil processing.
Examples of suitable synthetic carrier oils are polyolefins, (poly)esters, (poly)alkoxylates, and in particular aliphatic polyethers, aliphatic polyetheramines, alkylphenol-initiated polyethers and alkylphenol-initiated polyetheramines.
Adducts of butylene oxide with alcohols have excellent solubility in fuels but are comparatively expensive products and the starting material butylene oxide has to be prepared by a relatively expensive procedure.
More economical carrier oils can be made available in the form of adducts of propylene oxide with alcohols.
EP-A-0 704 519 describes propoxylates as carrier oil components in combination with a high molecular weight amine and a hydrocarbon polymer.
EP-A-0 374 461 describes such propoxylates for use as a carrier oil in combination with esters of mono- or polycarboxylic acids and alcohols or polyols and amino- or amido-containing detergents. EP-A-0 374 461 expressly states (cf. page 4, line 29 et seq.) that the sole use of the propoxylates described therein reduces the intake valve deposits only to an insufficient extent, namely to values of from 80 to 220 mg per valve.
However, the known additive systems of the prior art which contain carrier oils based on propylene oxide still do not have the optimum cleaning effect in the engine. Furthermore, such adducts of propylene oxide with alcohols often give rise to problems owing to their limited solubility in fuels and owing to their poor compatibility with other additives, so that separation may occur. This effect is displayed in a particularly dramatic way when additive concentrates—additive systems are usually marketed as such—are to be formulated.